A hollow molded article container of a resin, which is lightweight and has gas barrier properties, has recently been used for applications such as foods, beverages, industrial drugs, cosmetics, etc. For example, hollow molded article containers of ethylene-vinyl alcohol copolymer, vinylidene chloride, polyethylene terephthalate, etc. have been known.
However, hollow molded article containers obtained by blow molding these resins were not sufficient in heat resistance and gas barrier properties, In case that contents are charged in the container at elevated temperature or the container is washed with liquid of elevated temperature, the container of these resins is sometimes insufficient in heat resistance.
Unlike a crystalline polyester such as polyethylene terephthalate, polybutyrene terephthalate, etc., the liquid crystal polyester causes no entanglement in a molten state because of rigid-rod molecular shape, and shows such a behavior that a polydomain having a liquid crystal state under adequate temperature is formed and a molecular chain is oriented in a flow direction due to a low shear action. Therefore, it is normally referred to as a melting type liquid crystal (thermotropic liquid crystal) polymer.
It has hitherto been known that the liquid crystal polyester has a heat resistance and shows excellent gas barrier properties. However, the liquid crystal has a large anisotropy and a low melt viscosity and, therefore, it is extremely difficult to obtain a good hollow molded article container of the liquid crystal polyester due to blow molding.
Regarding a molded article container of the liquid crystal polyester or liquid crystal polyester resin composition, for example, a hollow molded article obtained by melt molding a resin composition comprising a liquid crystal polyester and a polyester having a specific structure is described in JP-A-61-192762.
In JP-A-2-263646 and JP-A-3-269054, a container having excellent gas barrier properties obtained by molding a blend of polyethylene terephthalate and a liquid crystal polyester is described.
In JP-A-1-289826, a molded article of a laminate comprising a polyethylene terephthalate layer and a liquid crystal polyester layer is described. In JP-A-4-166320, a method for producing a container of a liquid crystal polyester having a specific structure is described.
However, in any case, there are problems such as difficulty in producing a molded article container having an excellent appearance, low productivity, insufficient gas barrier properties of the container, etc. Therefore, requirements of the market are still to be satisfied.
In the field of the automobile industry, a gasoline tank made of plastic has recently been requested by the market in view of lightweight properties, moldability, strength, design freedom, etc, and it had been studied for years.
For example, polyethylene is superior in moldability, strength, etc., but is insufficient in gasoline barrier properties.
In JP-B-1-14049, a fuel tank of a multi-layer hollow molded article comprising a barrier layer of a material selected from polyamide, polyester and ethylene-vinyl acetate copolymer and a modified polyolefin layer is described.
In JP-A-4-47938, a fuel tank of a multi-layer hollow molded article comprising a polyamide layer, a high-density polyethylene layer and a modified high-density polyethylene layer is described.
However, these fuel tanks comprising the polyamide layer as the barrier layer are insufficient in gas barrier properties, and barrier properties to an alcohol-mixed fuel such as methanol-mixed fuel are further insufficient.
In JP-A-6-191296, an automobile fuel tank of a hollow molded article having a multi-layer structure comprising a copolymerized polyamide layer (of aromatic polyamide and nylon 6) as the barrier layer, a modified high-density polyethylene layer and a high-density polyethylene layer is described.
JP-A-6-218891 discloses a fuel tank of a multi-layer molded article comprising a barrier layer of a blend of polyethylene and polyamide.
In JP-A-7-52333, a fuel tank of a multi-layer structure comprising a layer of a resin composition of a thermoplastic resin and an ethylene-vinyl alcohol copolymer is described. In JP-A-7-40998, a flame retardant foamed plastic is described.
However, these fuel tanks were also insufficient in gasoline barrier properties or so-called barrier properties to gas hole, which is a mixture of gasoline and methanol, i.e. gas hole barrier properties. Furthermore, it was necessary to make a thickness of a resin layer extremely large so as to maintain high barrier properties.
Since the tank is a multi-layer structure, various problems such as interlayer peeling has still to be solved.